The present invention relates generally to a transport system for sequentially propelling photographic film through an automatic film processing machine.
In film processors for medical, graphic and photographic applications, there generally is a roller arrangement rack for moving the film through developer and fixer solutions.
As described in U.S. Pat. No. 3,656,676 (Hope), it is a practice in the industry to develop elongated film, such as 16millimeter, 35 millimeter, and 70 millimeter film, automatically by utilizing a plurality of side by side tanks and by employing film rack assemblies in conjunction with the processing tanks to direct the film through various stages of the development process.
In existing film processors, the rack assemblies utilize pairs of cooperating driven rollers to lead the film through the various development stages. Because of the length of the film, any small variation in the position of a roller will result in inconsistencies in processing over the length of film. This arrangement requires the total disassembly of the processor if an internal roller is out of position or malfunctions or needs cleaning. Total disassembly includes removing chain drivers, pulling gears off their roller shafts, and removing the entire side plates which hold the rollers. The procedure is time consuming and presents difficulties for the field service person.
Each film transport assembly has plastic hard rollers and rubber coated soft rollers to drive the film forward during the development process. In general, plastic is substantially cheaper than rubber by a factor of 10:1. However, the hard plastic rollers immerse in a fixer bath and electrostatic charges tend to electroplate silver onto the hard plastic rollers. This requires replacing the hard rollers to avoid artifacts forming on the outer circumference of the roller. Similarly, the rubber coated soft rollers grip the entry of the film into the transport and remove excess liquid on the surface of the film by squeezing the film at the exit. The rubber coated soft rollers swell in time from immersion into chemical processing liquids and require easy replacement. The wash transport and dryer transport are best suited for any squeezing action or vertical displacement of the film. A tangential force component is provided by the rubber to drive the film through the rollers. Therefore, pairs of scratch free and artifact free rollers are required to handle the x-ray film.
The gap between the rollers ranges from 0.002 to 0.010 inches depending on tolerances such as designed roller bearing centers, film thickness, gravity pressing the top roller on the film, and closing the gap to direct contact. Any excess pressure will mark and distort the soft gelatin emulsions in the developer solution. Normal x-ray film is 0.007 inches thick with emulsion on both sides.
Another problem associated with conventional roller transports, particularly a chain-driven roller transport, is inconsistencies in the final film product due to varying tension in the chain.
Another problem associated with conventional roller transports, particularly a belt driven roller transport, is that belt driven rollers transports are not equipped to handle single emulsion CRT recording film for medical use.